Single-use syringe

ABSTRACT

A syringe assembly comprises a barrel having an inside surface describing a chamber for retaining fluid. The barrel includes an open proximal end and a distal end with an elongated tip extending therefrom having a passageway therethrough in fluid communication with the chamber. A plunger rod includes an elongated body portion having a proximal end, a distal end and a stopper at the distal end. The stopper is slidably positioned in fluid-tight engagement within the barrel. An elongated projection extends distally outwardly from the distal end of the plunger rod. The elongated projection is shaped to fit within the passageway of elongated tip. Structure is provided to prevent the removal of a needle assembly from the elongated tip of the syringe barrel. A locking element is provided to prevent the proximal motion of the plunger rod with respect to the barrel after initial distal motion of the stopper to expel fluid from the syringe barrel.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to syringes and more particularly concerns disposable syringes having single-use and medication saving features.

2. Background

In the United States and throughout the world the multiple use of hypodermic syringe products which are intended for single use only is instrumental in drug abuse and in the transfer of contagious diseases. Intravenous drug users who routinely share and re-use syringes are a high risk group with respect to the AIDS virus. Also, the effects of multiple use are a major concern in some countries where repeated use of syringe products during mass inoculation programs may be responsible for the spread of many diseases. Re-use of single use hypodermic syringe assemblies is also instrumental in the spread of drug abuse even in the absence of infection or disease.

Many attempts have been made to remedy this problem. Most notable are early contributions which relied on a specific act to destroy the syringe after use either by using a destructive device or providing a syringe assembly with frangible zones so that the syringe could be rendered inoperable by the application of force. Other attempts involve the inclusion of structure which would allow the destruction or defeating of the syringe function through a conscious act by the syringe user. Although many of these devices work quite well they do require the specific intent of the user followed by the actual act to destroy or render the syringe inoperable. These devices are not effective with a user having the specific intent to re-use the hypodermic syringe. Accordingly, there is a need for a single use hypodermic syringe which becomes inoperative or incapable of further use automatically without any additional act on the part of the user. This automatic function is much harder to provide because the means for rendering the syringe inoperable must not prevent its filling or use under normal conditions.

In single-use syringes using needle assemblies having a hub attached to a needle cannula there is a need to prevent the removal of the needle assembly after the use of the single-use syringe so that the needle assembly cannot be used again with other syringes.

There is also a need in single-use syringes to minimize or eliminate wasted medication in the injection process. This is especially true in mass inoculation programs involving large numbers of people and in many cases limited financial resources. Medication which is not delivered, because it is trapped in the interior of the syringe tip after the plunger reaches its maximum distal displacement, can prove costly. Even with a small number of injections, an entire dose may be lost through medication which is trapped in the syringe and not delivered.

SUMMARY OF THE INVENTION

A syringe assembly comprises a barrel having an inside surface describing a chamber for retaining fluid. The barrel includes an open proximal end and a distal end with an elongated tip extending therefrom having a passageway therethrough in fluid communication with the chamber. A plunger rod includes an elongated body portion having a proximal end, a distal end and a stopper at the distal end. The stopper is slidably positioned in fluid-tight engagement within the barrel. An elongated projection extends distally outwardly from the distal end of the plunger rod. The elongated projection is shaped to fit within the passageway of elongated tip. Structure is provided to prevent the removal of a needle assembly from the elongated tip of the syringe barrel. A locking element is provided to prevent the proximal motion of the plunger rod with respect to the barrel after initial distal motion of the stopper to expel fluid from the syringe barrel.

One embodiment of the present syringe barrel assembly comprises a barrel having an inside surface defining a chamber for retaining fluid. The barrel has an open proximal end and a distal end. An elongated tip extending from the distal end and includes a passageway therethrough in fluid communication with the chamber. A collar surrounding the tip includes an inside surface and a discontinuity on the inside surface adapted to engage the hub of a needle assembly to prevent removal of the needle assembly from the tip of the syringe barrel. The discontinuity is configured to allow assembly of the needle assembly through axial motion of the hub with respect to the barrel. A plunger rod includes an elongated body portion having a proximal end, a distal end and a stopper at said distal end. The stopper is slidably positioned in fluid-tight engagement in the barrel. An elongated projection extends distally outwardly from the distal end of the plunger rod. The elongated projection is shaped to fit within the passageway of the elongated tip. A locking element is positioned in the barrel between the elongated body portion of the plunger rod and the inside surface of the barrel. The element includes a proximal portion and a distal portion. The element further includes a proximally and outwardly facing locking barb, a distally and inwardly facing resisting edge and an inwardly facing driving edge at the proximal portion of the element. The driving edge is adapted to interact with the body portion of the plunger rod to move the locking element along the barrel as the stopper is advanced along the barrel. The resisting edge and the barb are adapted to prevent proximal motion of the plunger rod with respect to the barrel after initial distal motion of the plunger rod to expel fluid through the passageway wherein subsequent proximal motion of the plunger rod with respect to the barrel causes the resisting edge to engage the plunger rod causing the locking element to move in a proximal direction wherein the locking barb engages the inside surface of the barrel to prevent further movement and allowing only distal movement of the plunger rod with respect to the barrel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the single-use syringe assembly of the present invention with a needle assembly.

FIG. 2 is a partial cross-sectional view of the syringe assembly of FIG. 1 taken along line 2--2.

FIG. 3 is a cross-sectional view of the syringe assembly of FIG. 2 taken along line 3--3.

FIG. 4 is an enlarged partial cross-sectional perspective view of a portion of the syringe assembly of FIG. 1 containing the locking element.

FIG. 5 is an enlarged top plan view of the locking element illustrating details of the locking element before forming.

FIG. 6 is a side-elevational view of the locking element.

FIG. 7 is a side-elevational view of the end of the locking element of FIG. 6.

FIGS. 8-11 illustrate the assembly and use of the single-use syringe assembly.

FIG. 12 is an enlarged partial cross-sectional view of the single-use syringe assembly of FIG. 11.

FIG. 13 is a side-elevational view of an alternative plunger rod assembly for use in the present invention.

FIG. 14 is a cross-sectional view of the plunger rod assembly of FIG. 12 taken along line 13--13.

DETAILED DESCRIPTION

While this invention is satisfied by embodiments in many different forms, there is shown in the drawings and will herein be described in detail preferred embodiments of the invention with the understanding that the present disclosure is to be considered as exemplary of the principles of the invention and is not intended to limit the invention to the embodiments illustrated. The scope of the invention will be measured by the appended claims and their equivalents.

For the purposes of the description of the present invention, the term "distal end" is meant to refer to the end furthest from the person holding the syringe, whereas the term "proximal end" is meant to refer to the end closest to the holder of the syringe.

Adverting to FIGS. 1-12, a syringe assembly 20 having single use features, includes a barrel 21 having an inside surface 22 describing a chamber 23 for retaining fluid. Barrel 21 includes an open proximal end 25 and a distal barrel end 27. An elongated tip 29 extends distally outwardly from the distal end of the barrel and includes a passageway 28 therethrough in fluid communication with chamber 23.

Syringe barrel 21 further includes a collar 24 having an inside surface 26. The inside surface further includes a discontinuity, which in this embodiment is an inwardly directed radial projection which extends around the entire inside surface to form annular ring 30.

Syringe assembly 20 is preferably provided with a needle assembly 100 including a cannula 101 having a proximal end 102, a distal end 103 and a lumen therethrough. A hub 105 includes an open proximal end 106 with a cavity 107 therein and a distal end 108 joined to the proximal end of the cannula so that the lumen is in fluid communication with the cavity of the hub. The hub further includes an outwardly directed projection 109 on its proximal end. When needle assembly 100 is connected to syringe barrel 21 elongated tip 29 of the barrel is positioned within cavity 107 of the hub and outwardly projection 109 has passed over the discontinuity in the collar and is adjacent thereto. The discontinuity helps prevent removal of the needle assembly from the elongated tip.

Syringe barrels commonly include a collar around the distal tip having a thread on the internal surface of the collar. This configuration is often referred to as a locking luer collar. A needle assembly having a hub with outwardly extending projections is placed on the distal end of the syringe by aligning the distal tip of the syringe with a cavity in the hub and moving the needle assembly toward the syringe barrel so that the outward projections on the hub engage the thread. The needle assembly is then rotated or screwed onto the locking luer collar so that the needle assembly is held tightly on the distal tip of the syringe barrel through the interaction of the locking luer collar and the projections on the hub. This is an excellent structure for most applications since it allows for applying the appropriate size needle assembly at the time of use and for changing needle assemblies during a procedure which may require two or more different sizes. However, for a single-use application it is not desirable to have structure which provides for the removal of the needle assembly. The present invention provides structure to prevent re-use of the syringe or any of its components, including the needle assembly. A preferred structure to prevent removal of the needle assembly is to provide a discontinuity on the inside surface of the collar which is configured to interfere with the outwardly directed projection or projections on the needle hub. Accordingly, during assembly of the needle assembly to the syringe barrel the projections on the hub will snap over the discontinuity in the collar. It is easy to install a needle assembly in this fashion since the needle assembly is usually provided with the needle shield which can be used to apply proximally directed pressure for installing the needle assembly. However, the needle shield is not effective in applying distally directed force since it will come off the needle assembly as it is intended to do when distally directed forces are applied. Further, the shape of the discontinuity and/or the shape of the outwardly directed projections on the needle hub can be made to be tapered or configured so that installation forces are substantially less than removal forces. It is preferred that the discontinuity and the outwardly directed projection on the hub are configured to allow assembly of the needle assembly to the barrel without a twisting motion and only with axial motion of the components. At the very least, the needle assembly can no longer be removed by simple rotation of the needle hub and will require the use of tools or extraordinary force which may damage the syringe in order to remove the needle assembly. This is an important feature of the present invention since it protects people from problems associated with multiple use by helping to prevent easy re-use of the needle assembly on another syringe.

It is within the purview of the present invention to include many shapes for the discontinuity on the interior of the collar and the projections on the hub so long as the needle assembly cannot be easily unscrewed or removed from the syringe barrel. A full annular ring on the inside of the collar is preferred. However, for manufacturing reasons and depending on the shape of the hub, it may be more desirable to have an inwardly directed radial projection which is less than a full annular ring. The discontinuity may also be recessed in the inside surface of the collar. Also, it is within the purview of the present invention to include interacting structure between the tip and the syringe barrel and the cavity in the hub to achieve the same result.

A plunger 32 includes a stopper 39 and a plunger rod 33 having an elongated body portion 34. The elongated body portion includes a longitudinal recess 35, a proximal end 37, and a distal end 38. In this preferred embodiment the longitudinal recess is v-shaped when viewed along the longitudinal axis of elongated body portion 34 with the narrowest portion of the recess being closest to the center or longitudinal axis of the elongated body portion. Stopper 39 is positioned at distal end 38 of the plunger rod and is preferably integrally formed with the plunger rod. The stopper is slidably positioned in fluid-tight engagement in the barrel while a portion of body portion 34 of the plunger rod extends outwardly from open proximal end 25 of the barrel. The plunger rod is accessible outside of open proximal end 25 of the barrel and is provided to move the stopper along the barrel to force fluid into and out of the chamber 23 through passageway 28. Disc-shaped plunger rod flange 40 is provided as a convenient structure for applying forces to move the plunger rod with respect to barrel 21. A flange 41 is also provided at the proximal end of the barrel to facilitate handling and positioning the syringe and for maintaining the relative position of the barrel with respect to the plunger rod during filling and medication administration.

It is within the purview of the present invention to include plunger rods and stoppers which are separately formed or integrally formed of the same material or different materials, such as in two-color molding, or separately formed of the same or different materials and joined together by mechanical means, adhesive, ultrasonic welding, heat sealing or other suitable means. It is understood that the plunger rod assembly of this preferred embodiment is merely illustrative of these many possibilities.

An elongated projection 36 extends distally outwardly from distal end 38 of plunger rod 33. Elongated projection 36 is shaped to fit within passageway 28 of elongated tip 29. This is an important feature of the present invention because the elongated projection moves additional volume of medication out of the syringe chamber which is preferably approximately equal to the volume of the elongated projection. This feature substantially eliminates wasted medication which would normally be left in the syringe barrel after the plunger rod is moved to its distal-most position within the syringe barrel. It is preferred that the distal end of the plunger rod and/or the stopper be configured to match the interior structure of the barrel and that the elongated projection be similarly shaped to the interior passageway of the syringe barrel tip so that there is little space between these components in order to maximize the amount of medication which is injected and minimize the amount of medication which remains in the syringe barrel after injection. In this preferred embodiment, stopper 39 is integrally molded with plunger rod 33 and elongated projection 36 resulting in a one-piece plunger 32. As indicated above, it is within the purview of the present invention to include a separate stopper. When a separate stopper is included the elongated projection may be integrally formed or attached to the stopper or, as will be explained in more detail hereinafter, the separate stopper may include an aperture through which the elongated projection extends. This important feature of the present invention not only results in substantial savings for mass inoculations or other programs involving many syringes but it also reduces the incentive for improper tampering of the syringe since little or no medication remains in the syringe after injection. This feature is particularly desirable if the medication is a narcotic or other addicting substance because residual amounts of medication after injection are not desirable.

A locking element 42 is positioned in the barrel and partially within longitudinal recess 35 between the plunger rod and the inside surface 22 of the barrel. Longitudinal recess 35 of the plunger rod acts as a pathway for longitudinal motion of the locking element relative to the elongated body portion of the plunger rod. Element 42 includes a proximal portion 44. Proximal portion 44 includes a proximally and outwardly facing locking barb 46. In addition proximal portion 44 also includes two additional anti-twist locking barbs 47 and 49 which are preferably not facing in the same direction as locking barb 46. Locking barbs 47 and 49 are optional but important in helping prevent misuse of the instant syringe to overcome the single use function by twisting the plunger rod as will be explained in more detail hereinafter.

It is preferred that locking barb 46 remain in the plane of sheet metal 43 while anti-twist locking barbs 47 and 49 are positioned at angles with respect to the locking barb preferably with each anti-twist locking barb being angled away from the locking barb 46 on different sides of the locking barb as best illustrated in FIG. 6. Where anti-misuse features are desirable it is preferred that at least two proximally and outwardly facing non-parallel locking barbs are provided. If two barbs are used it is preferable that these barbs are included with respect to each other at an angle within the range of about five (5) degrees to ninety (90) degrees.

It is desirable that three barbs are provided with one of the three locking barbs remaining substantially parallel to the body structure or in the plane of the body material, and the other two barbs being bent at angles away from this barb. It is desired but not necessary, if sheet material construction is used for the locking element, that one of the locking barbs should be oriented in the plane of the sheet material. The second locking barb or first anti-twist locking barb is preferably located in a plane positioned at an angle of between about five (5) degrees to ninety (90) degrees with respect to the plane of locking barb and the third locking barb or second anti-twist locking barb is located in a plane positioned at an angle of between about five (5) degrees and ninety (90) degrees with respect to the plane of the locking barb and preferably oriented toward the opposite side of the plane of the locking barb as the first anti-twist locking barb. For the purposes of the present invention the non-parallel relationship of the barbs, when the locking element is made of sheet metal, is established by bending one or more of the barbs so that the barbs point in different directions as a result of the barb or barbs being bent.

Locking element 42 also includes a distally and inwardly facing resisting edge 50 and an inwardly facing driving edge 52 at proximal portion 44 of the locking element. For the purpose of describing locking element 42 the term "inwardly" shall mean toward a surface on the plunger rod body portion such as a surface along longitudinal groove 35, and the term "outwardly" shall mean facing generally toward inside surface 22 of barrel 21. Driving edge 52 is adapted to interact with longitudinal recess of the plunger rod to move the locking element along the barrel as the stopper is advanced along the barrel by force applied to the plunger rod. As will be explained in more detail hereinafter, driving edge 52 also, because of its orientation, allows proximal motion of the plunger rod with respect to the barrel during filling while helping to keep the locking element in a fixed position with respect to said barrel. Resisting edge 50 and the locking barbs are adapted to prevent proximal motion of plunger rod 33 with respect to barrel 21 after initial distal motion of the stopper on the plunger rod to expel fluid through passageway 28. Subsequent proximal motion of the plunger rod with respect to the barrel causes resisting edge 50 to engage elongated body portion 34 in the longitudinal recess 35 causing locking element 42 to move in a proximal direction wherein the locking barb 46 engages inside surface 22 of the barrel to prevent further movement and allowing only distal movement of the plunger rod with respect to the barrel.

In this preferred embodiment locking element 42 further includes a second inwardly facing driving edge 53 at proximal portion 44 and a second proximally and outwardly facing locking barb 56 adjacent to additional anti-twist locking barbs 57 and 59 which are angularly oriented away from second locking barb 56 and preferably non-parallel with respect to each other. Locking barbs 46, 47 and 49 and driving edge 52 are separated from second locking barbs 56, 57 and 59 and second driving edge 53 by longitudinal gap 61 so that driving edge 52 and second driving edge 53 extend proximally in cantilever spring-like fashion from distal portion 45 acting to force locking barb 46 and second locking barb 56 against the inside surface of the barrel. As will become more apparent hereinafter it is preferable to have a locking element with spring-like qualities such as a locking element formed of metal such as berelieum copper or stainless steel with stainless steel sheet metal being preferred for medical applications. It is preferred that the stainless steel sheet metal have a thickness of between about 0.003 inch (0.076 mm) to 0.20 inch (0.508 mm) when used in a syringe barrel having an inside diameter of about 0.333 inch (8.5 mm). Longitudinal gaps 61 divides proximal portion 44 into two cantilever spring arms 62 and 63 which are preferably bent along preferably variable radius R so that the distance across the locking element at the locking barbs is larger than the space available between the plunger rod and the inside surface of the syringe barrel. This configuration requires compression of the spring arms upon assembly and, as will be explained in more detail hereinafter, provides a slight pressure of the locking barbs against the inside surface of the barrel.

The syringe of the present invention may be used with a plurality of locking elements, for example, the preferred embodiment will accept up to four separate locking elements to provide additional mechanical resistance to multiple use. Also, a locking element and/or plunger rod may be shaped so that a single larger locking element engages areas further apart on the inside surface of the syringe barrel such as along 90 degrees to 360 degrees of the inside diameter of a circularly shaped syringe barrel.

An important feature of the instant invention is its ability to provide a syringe assembly having structure for limiting the volume of fluid with which can be taken into the chamber through passageway 28 and subsequently delivered. This feature assists in achieving substantially consistent delivery volumes from syringe to syringe and is useful in programs involving large numbers of subjects being injected with medication at the same time such as immunization programs. This feature also prevents misuse by limiting the volume the syringe assembly is capable of delivering. To limit delivery volume a barrier means such as delivery limiting barrier 65 is provided. Delivery limiting barrier 65 establishes the maximum proximal position of locking element 42 with respect to the elongated body portion of the plunger rod. The barrier function can be accomplished by various structures such as a raised rib positioned transversely along the surface of the plunger rod in the area of the longitudinal recess as will be described hereinafter. As the plunger rod is moved in a proximal direction along the barrel the locking element because of its spring action which forces the locking barbs against the inside surface of the barrel tends not to move with the plunger rod. The delivery limiting barrier provides an obstacle in longitudinal recess 35 over which locking element 42 cannot pass. Accordingly, when the locking element contacts delivery limiting barrier 65 it is forced along the barrel with the plunger rod. The delivery limiting barrier in this embodiment is a circular flange. It is within the purview of the instant invention to include barrier means which is fixed to the plunger rod such as delivery limiting barrier 65 or movable thereon to adjust the volume of the syringe. The instant invention also functions without barrier means wherein the volume chosen is visually determined through use of a graphic scale printed on the syringe barrel (not shown) or other means.

Another important feature of the instant invention which helps provide consistently uniform syringe assembly performance through large quantities of syringe assemblies is the inclusion of a ledge such as delivery ledge 67 running transversely across longitudinal recess 35. Delivery ledge 67 includes inclined surface 68 and vertical edge wall 69. Delivery ledge 67 is positioned at a distance which is approximately the overall length of the locking element from the proximal side of the stopper or any structure in the longitudinal recess defining the proximal most limit of the recess, such as wall 30. Delivery ledge 67 in the preferred embodiment is positioned at a distance of approximately the length of the locking element proximally from wall 130 so that edge wall 69 is positioned at a distance slightly longer than the length of the locking element from wall 130. Delivery ledge 67 is lower and less pronounced than the delivery limiting barrier because it is configured to allow the locking element to pass thereover when the locking element moves distally with respect to the plunger rod but to positively engage driving edges 52 and 53 with vertical edge wall 69 when the element moves proximally with respect to the plunger rod. In this preferred embodiment the delivery ledge is formed by a recessed-groove in recess 35, however, it is also within the purview of the instant invention to include a delivery ledge formed of a raised projection such as a raised rib.

Initially, the locking element will slide along the longitudinal recess of the plunger rod while air is being forced from the chamber through the passageway in the needle cannula until the locking element abuts against delivery limiting barrier 65. Then the locking element will move with the plunger rod toward the distal end of the syringe barrel. In use, when drawing medication into the chamber through the needle cannula, the plunger rod will move in a proximal direction while the locking element will tend to remain stationary with respect to the barrel until it abuts against support wall 30. This position, as will be explained in more detail hereinafter, defines the maximum volume of the syringe. At this point, medication may be delivered from the syringe by moving the plunger rod in a distal direction with respect to the barrel such as by applying force to disc-shaped plunger rod flange 40. As the plunger rod moves toward the distal end of the barrel driving edges 52 and 53 tend to engage the plunger rod surface in the longitudinal recess and travel with the plunger rod. In almost all cases this phenomenon will occur readily because of the higher hardness of the locking element which is forced by its spring action against the plunger rod longitudinal recess. However, to assure that reliable and consistent operation from syringe assembly to syringe assembly delivery ledge 67 through its vertical ledge 69 further facilitates the engagement of driving edges 52 and 53 and the plunger rod longitudinal recess 35. It is desirable to shape the delivery ledge so that portions of the locking element pass readily over it when the locking element moves distally with respect to the plunger rod but to engage the driving edges 52 and 53 when the motion is reversed. To this end delivery ledge 67 is shaped to have inclined surface 68 at is distal side and vertical edge wall 69 at its proximal side. It is also within the purview of this invention to include a delivery ledge which is raised from the surface of the plunger rod longitudinal recess 35 to accomplish the same result.

A tamper resistant barrier 71 is positioned transversely with respect to the plunger rod wall to block access to the locking element through open end 25 of the barrel in order to prevent unwanted tampering with the locking element to defeat the single use function of the instant invention. It may be possible to use a long instrument such as forceps to reach in and disengage the locking element or to forcibly remove it. Tamper resistant barrier 71 acts to prevent this access. In the preferred embodiment, although it is not necessary, the tamper resistant barrier 71 and delivery limiting barrier 65 occupy the same position along the axial length of the plunger rod. A different embodiment of the plunger rod wherein the delivery limiting barrier and the tamper resistant barrier are at separate positions along the plunger rod will be described hereinafter.

Another feature of the instant invention which helps prevent misuse is the inclusion of a weakening means located between tamper resistant barrier 71 and the proximal end of the plunger rod. In this preferred embodiment the weakening means includes an area of reduced transverse cross-sectional thickness 73, which helps to allow the plunger rod to break if excessive and unnecessary amounts of force are applied at the proximal end. A person attempting to defeat the single use function of the instant invention may attempt to do so by twisting or bending the plunger rod in order to distort or defeat the locking element. To avoid this possibility the area of reduced transverse cross-sectional thickness in the plunger rod will greatly reduce the resistance of the plunger rod to bending or torsional forces causing it to fail.

To further resist torsional force supplied to the proximal end of the plunger rod and in order to promote failure of the plunger rod at the area of reduced transverse cross-sectional, thickness anti-twist locking barbs 47 and 49 and additional anti-twist locking barbs 57 and 59 which are angled out of the plane of locking barbs 46 and 56 respectively are oriented to dig into the syringe barrel wall upon the application of torsional force. For example, anti-twist locking barbs 47 and 57 would tend to resist torsional rotation in one direction while anti-twist locking barbs 49 and 59 would tend to resist torsional rotation of the plunger rod with respect to the barrel in the opposite direction.

Referring now to FIGS. 8-11 the syringe assembly of the instant invention may be assembled by placing the stopper in the barrel with the plunger rod projecting outwardly from open end 25 of the barrel and then placing locking element 42 in the longitudinal recess in a position which is distal to delivery limiting barrier 65 and then forcing the stopper and plunger rod along the barrel until the stopper is in about its distal-most position. During motion of plunger rod 33 locking element 42 will, because of its spring action and locking barbs, remain substantially in one position with respect to the barrel until driving edges 52 and 53 contact delivery limiting barrier 65 and causes the locking element to move with the plunger rod to the position illustrated in FIG. 9. At this time the cannula, if it is not already in fluid communication with a source of medication, may be placed in a stoppered vial containing medication to be injected (not shown) and the plunger rod withdrawn so that medication 74 is drawn into the chamber as best illustrated in FIG. 10. During the step of drawing medication into the chamber the locking element 42 remains in a fixed position with respect to the barrel. This position of the locking element relative to the barrel defines the maximum volume which the syringe assembly will deliver and is established when support wall 130 of the plunger rod contacts resisting edge 50 of the locking element. Further proximal motion of the plunger rod will not occur because the locking element barbs will engage barrel inside surface 22 to resist this motion. The syringe is now ready for administering medication to a patient using known safe procedures. After the medication 74 is expelled from the syringe through passageway 28 and cannula 101 the syringe assembly of the instant invention will be in the position illustrated in FIG. 11. While medication is being delivered the locking element will move with the plunger rod along the barrel in a proximal direction because driving edges 52 and 53 are engaging the plunger rod with enough force to prevent any slipping. To facilitate the motion of locking element 42 toward the distal end of the barrel delivery ledge 67 is provided on the preferred embodiment to help improve the engagement between driving edges 52 and 53 and the plunger rod.

After delivery of the medication stopper 39 and plunger rod 33 are at about their distal-most position with respect to barrel 21. Withdrawal of the plunger rod from the barrel may not take place because at this position the proximally and outwardly facing locking barbs are engaging the barrel preventing proximal motion of the locking element with respect to the barrel while the locking element is resisting proximal motion of the plunger rod with respect to the barrel through, in this preferred embodiment, contact between resisting edge 50 of the locking element and support wall 30 of the plunger rod. The syringe of the instant invention has been used once and cannot be used again and can be properly discarded. Any attempt to dislodge the locking element by applying torsional force to the plunger would will be resisted by the locking element and possibly cause the plunger rod to fracture or break at the area of reduced transverse cross-sectional thickness 73. Also, an attempt to subsequently remove or disarm the locking element will be resisted by tamper resistant barrier 71.

Adverting now to FIGS. 12 and 13, an alternative embodiment of the plunger rod and stopper of the instant invention is illustrated. In this embodiment the barrel and locking element although not shown are identical to the embodiment of FIGS. 1-11. In this embodiment an alternative plunger rod and stopper assembly 80 includes a plunger rod 81 having a proximal end 83 and a distal end 85. A stopper 139 at distal end 85 is slidably positioned in fluid-tight engagement in the barrel (not shown). Plunger rod 81 includes an elongated projection 136 extending distally outwardly from the distal end of the plunger rod. The elongated projection is shaped to fit within the passageway of the elongated tip of the syringe barrel (not shown). In this embodiment, stopper 139 is a separate element made of elastomeric material. Elongated projection 136 projects through aperture 131 and stopper 139 and is formed integrally with plunger rod 81. The elongated projection could also be integrally formed of the elastomeric material of the separate stopper.

Plunger rod 81 includes barrier means on the body portion for limiting the delivery volume of the syringe assembly by establishing the maximum proximal position of the locking element (not shown) with respect to elongated body portion 82 of the plunger rod. In this embodiment barrier means includes raised rib 86 running transversely across longitudinal recess 135 of elongated body portion 82. The plunger rod also includes stopper support means including wall 132 adjacent to stopper 139 for supporting the stopper during distal motion of the stopper with respect to the barrel. Wall 132, in this embodiment, is a support flange positioned transversely with respect to longitudinal axis 87 of elongated body portion 82. The plunger rod also includes tamper resistant barrier 88 in the shape of a barrier flange positioned transversely with respect to longitudinal axis 87. An area of reduced transverse cross-sectional thickness 173 is also provided in a position which is proximal to tamper resistant barrier 88 for allowing twisting failure of the plunger rod on application of excessive force to proximal end 83 of the plunger rod. Plunger rod 81 also includes delivery ledge 91 in the form of a raised projection running transversely along longitudinal recess 35a. Delivery ledge 91 includes inclined surface 92 and vertical edge wall 93. Delivery ledge 91 in this embodiment is positioned so that the distance between support wall 132 and vertical edge wall 93 is slightly larger than the length of the locking element (not shown). As with the embodiment of FIGS. 1-11, the positioning of the delivery ledge is determined by the distance between the support wall and the vertical edge wall.

The syringe barrel of the present invention may be constructed of a wide variety of rigid materials with thermoplastic materials such as polypropylene and polyethylene being preferred. Similarly thermoplastic materials such as polypropylene, polyethylene and polystyrene are preferred for the plunger rod. A wide variety of materials such as natural rubber, synthetic rubber and thermoplastic elastomers are suitable for the stopper. The choice of stopper material will depend on compatibility with the medication being used. In the preferred embodiment of this invention the stopper, made of medical grade rubber, includes a partially hollow interior with an undercut ledge which is snap fit over a complementary structure on the plunger rod to secure the stopper to the plunger rod. A stopper and plunger rod may also be integrally formed of the same material or of different materials.

As previously recited, it is preferable that the locking element being fabricated from a material which is harder than the barrel and plunger rod material so that the locking barbs and resisting edge and driving edge may effectively engage these components. Resilient spring-like properties are also desirable along with low cost dimensionally consistent fabrication. With this in mind, sheet metal is the preferred material for the locking element with stainless steel being preferred for medical applications. Although the locking element of the preferred embodiment is fabricated from a single sheet, it is within the purview of the instant invention to include locking elements made of other forms of material such as wire and locking elements containing multiple parts and apparatus such as hinges and springs to achieve the function of the preferred locking element. 

What is claimed is:
 1. A syringe assembly comprising:a barrel having an inside surface describing a chamber for retaining fluid, said barrel having an open proximal end and a distal end, and an elongated tip extending from said distal end having a passageway therethrough in fluid communication with said chamber; a plunger rod including an elongated body portion having a proximal end, a distal end, and a stopper at said distal end, said stopper being slidably positioned in fluid-tight engagement in said barrel, an elongated projection extending distally outwardly from said distal end of said plunger rod, said elongated projection being shaped to fit within said passageway of said elongated tip, said body portion extending outwardly from said open proximal end of said barrel; a collar surrounding said tip having an inside surface and a discontinuity on said inside surface adapted to engage the hub of a needle assembly to help prevent removal of the needle assembly from said tip, said discontinuity being configured to allow assembly of the needle assembly through axial motion of the hub; and a locking element positioned in said barrel between said elongate body portion of said plunger rod and said inside surface of said barrel, said element having a proximal portion and a distal portion, said locking element including a proximally and outwardly facing locking barb, a distally and inwardly facing resisting edge and an inwardly facing driving edge at said proximal portion of said element, said driving edge adapted to interact with said body portion of said plunger rod to move said locking element along said barrel as said stopper is advanced along said barrel, said resisting edge and said barb adapted to prevent proximal motion of said plunger rod with respect to said barrel after initial distal motion of said stopper to expel fluid through said passageway wherein subsequent proximal motion of said plunger rod with respect to said barrel causes said resisting edge to engage said plunger rod causing said locking element to move in a proximal direction wherein said locking barb engages said inside surface of said barrel to prevent further movement and allowing only distal movement of said plunger rod with respect to said barrel.
 2. The syringe assembly of claim 1 further including a needle assembly including a cannula having a proximal end, a distal end and a lumen therethrough, a hub having an open proximal end with a cavity therein, and a distal end joined to said proximal end of said cannula so that said lumen is in fluid communication with said cavity, and an outwardly directed projection on said proximal end of said hub, said needle assembly being connected to said barrel so that said elongated tip of said barrel is in said cavity of said hub and said outwardly directed projection on said hub is adjacent to said discontinuity in said collar.
 3. The syringe assembly of claim 2 wherein said needle assembly includes a second outwardly directed projection on the proximal end of said hub.
 4. The syringe assembly of claim 2 wherein said outwardly directed projection on said hub extends substantially around the periphery of said hub.
 5. The syringe assembly of claim 1 wherein said discontinuity on said inside surface of said collar comprises an inwardly directed radial projection.
 6. The syringe assembly of claim 5 wherein said radial projection is an annular ring.
 7. The syringe assembly of claim 1 wherein said stopper is made of elastomeric material.
 8. The syringe assembly of claim 7 wherein said elastomeric material is selected from the group of natural rubber, synthetic rubber, thermoplastic elastomers and combinations thereof.
 9. The syringe assembly of claim 1 further including barrier means on said body portion for limiting the delivery volume of said syringe assembly by establishing the maximum proximal position of said locking element with respect to said elongate body portion.
 10. The syringe assembly of claim 1 wherein said elongate body portion includes a longitudinal recess, said recess acting as a pathway for the longitudinal motion of said locking element relative to said elongate body portion between said stopper and said barrier means.
 11. The syringe assembly of claim 10 wherein said longitudinal recess is v-shaped when viewed along the longitudinal axis of said body portion with the narrowest portion of said recess being closest to the center of the body portion.
 12. The syringe assembly of claim 10 further including a delivery ledge in said recess for engaging said driving edge when said locking element is in about its furthest most distal position with respect to said recess for assuring distal motion of said locking element as said plunger moves distally along said barrel to expel fluid from said chamber.
 13. The syringe assembly of claim 1 wherein said locking element includes a second proximally and outwardly facing locking barb and a second inwardly facing driving edge at said proximal portion of said element.
 14. A syringe assembly comprising:a barrel having an inside surface describing a chamber for retaining fluid, said barrel having an open proximal end and a distal end, a elongated tip extending from said distal end having a passageway therethrough in fluid communication with said chamber; a plunger rod including an elongated body portion having a proximal end, a distal end, and a stopper at said distal end, said stopper being slidably positioned in fluid-tight engagement in said barrel, an elongated projection extending distally outwardly from said distal end of said plunger rod, said elongated projection being shaped to fit within said passageway of said elongated tip said body portion extending outwardly from said open barrel end; means for preventing proximal motion of said plunger rod with respect to said barrel after distal motion of said stopper to expel fluid through said passageway; a needle assembly including a cannula having a proximal end, a distal end and a lumen therethrough, a hub having an open proximal end with a cavity therein, a distal end joined to said proximal end of said cannula so that said lumen is in fluid communication with said cavity, said needle assembly being connected to said barrel so that said elongate tip of said barrel is in said cavity of said hub; and means for preventing removal of the needle assembly from said barrel including a collar surrounding said tip having an inside surface, and a discontinuity on said inside surface adapted to engage the hub of a needle assembly to prevent removal of the needle assembly away from said tip and said hub further including an outwardly directed projection on said proximal end, said needle assembly being connected to said barrel so that said outwardly directed projection on said hub is adjacent to said discontinuity and said collar.
 15. A syringe assembly comprising:a barrel having an inside surface describing a chamber for retaining fluid, said barrel having an open proximal end and a distal end, and a elongated tip extending from said distal end having a passageway therethrough in fluid communication with said chamber, a collar surrounding said tip having an inside surface, and a discontinuity on said inside surface adapted to engage the hub of a needle assembly to prevent removal of the needle assembly away from said tip, said discontinuity being configured to allow assembly of the needle assembly to said barrel through axial motion of the hub toward the barrel; a plunger rod including an elongated body portion having a proximal end, a distal end, and a stopper at said distal end integrally formed with said stopper, said stopper being slidably positioned in fluid-tight engagement in said barrel, an elongated projection extending distally outwardly from said distal end of said plunger rod, said elongated projection being shaped to fit within said passageway of said elongated tip, said body portion extending outwardly from said open proximal end of said barrel; and a locking element positioned in said barrel between said elongate body portion of said plunger rod and said inside surface of said barrel, said element having a proximal portion and a distal portion, said locking element including a proximally and outwardly facing locking barb, a distally and inwardly facing resisting edge and an inwardly facing driving edge at said proximal portion of said element, said driving edge adapted to interact with said body portion of said plunger rod to move said locking element along said barrel as said stopper is advanced along said barrel, said resisting edge and said barb adapted to prevent proximal motion of said plunger rod with respect to said barrel after initial distal motion of said stopper to expel fluid through said passageway wherein subsequent proximal motion of said plunger rod with respect to said barrel causes said resisting edge to engage said plunger rod causing said locking element to move in a proximal direction wherein said locking barb engages said inside surface of said barrel to prevent further movement and allowing only distal movement of said plunger rod with respect to said barrel. 